We present a new dataset analysis of the neutrino experiment at the Baksan Underground Scintillator Telescope with muon energy threshold about 1 GeV for the longest exposure time toward the Sun. In search for a signal from self-annihilations of dark matter particles in the center of the Sun we use an updated sample of upward through-going muons for 24.12 years of live time. No observable excess has been found in measured muons relative to expected background from neutrinos of atmospheric origin. We present an improved data analysis procedure and describe it in detail. We set the 90% C.L. new upper limits on expected neutrino and muon fluxes from dark matter annihilations in the Sun, on the corresponding annihilation rates and cross sections of their elastic scattering off proton.Keywords: high energy neutrinos, dark matter. †Dedicated to the memory of Stas Mikheyev.

We have analyzed a data set taken over 2.76 years live time with the Baikal neutrino telescope NT200. The goal of the analysis is to search for neutrinos from dark matter annihilation in the center of the Sun. Apart from the conventional annihilation channels bb, W + W − and τ + τ − we consider also the annihilation of dark matter particles into monochromatic neutrinos. From the absence of any excess of events from the direction of the Sun over the expected background, we derive 90% upper limits on the fluxes of muons and muon neutrinos from the Sun, as well as on the elastic cross sections of dark matter scattering on protons.

We propose general semiclassical method for computing the probability of soliton-antisoliton pair production in particle collisions. The method is illustrated by explicit numerical calculations in (1 + 1)-dimensional scalar field model. We find that the probability of the process is suppressed by an exponentially small factor which is almost constant at high energies.Ever since the discovery of topological solitons, a question remains [1, 2] of whether soliton-antisoliton (SA) pair can be produced at sizable probability in collision of two quantum particles. This process, which involves a transition from perturbative two-particle state to a nonperturbative state containing SA pair, eludes treatment by any of the standard methods. A general expectation [1,3] is that the probability of the process is exponentially suppressed in weak coupling regime,where E is the total energy, g ≪ 1 is the coupling constant. Indeed, crudely speaking, one can think of solitons as bound states of N S ∼ 1/g 2 particles [1]. Then the suppression (1) is due to multiparticle production [3]. In this Letter we propose general semiclassical method for computing the leading suppression exponent F (E) of the inclusive process "two particles → SA pair + particles." As a by-product, we calculate the exponent F N (E) of the same process with N initial particles. In our method the problem is deformed by introducing a small parameter δρ which turns the process of SA pair production into a well-known tunneling process. To the best of our knowledge, no method of this kind has ever been proposed before.For definiteness we consider (1 + 1)-dimensional scalar field theory with action [4]This model possesses topological solitons if the scalar potential V (φ) has a pair of degenerate minima φ − and φ + , see the inset in Fig. 1, solid line. Soliton and antisoliton solutions interpolate between the minima; their profiles are shown in Fig. 2a. An obstacle to the semiclassical description of SA pair production is related to the fact that soliton and antisoliton attract each other and annihilate classically into N SA ∼ 1/g 2 particles. Thus, there is no potential barrier separating SA pair from the particle sector and the process under study cannot be treated as potential tunneling.We get around this obstacle by introducing the potential barrier between SA pair and perturbative states. Namely, we add negative energy density (−δρ) to the vacuum φ + , see dashed line in the inset in Fig. 1. This turns φ − and φ + into false and true vacua, respectively; the process of SA pair production is now interpreted as false vacuum decay [5] induced by particle collisions. The latter is a well-studied tunneling process [6,7]. In the end of calculation we will take the limit δρ → 0.The height of the potential barrier between the false and true vacua is given by the energy E cb of the critical bubble [5] -unstable static solution "sitting" on top of the barrier. The pressure δρ inside this bubble is balanced by the soliton-antisoliton attraction. Let us estimate the criti...

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF’s physics potential.

We present a calculation of the branching ratio of orthopositronium decay into an invisible mode, which is done in the context of Mirror World models, where ordinary positronium can disappear from our world due to oscillation into its mirror twin. In this revision we clarify some formulas and approximations used previously, correct them at some places, add new effects relevant for a feasible experiment and finally perform a combined analysis. We include into consideration various effects due to external magnetic and electric fields, collisions with cavity walls and scattering off gas atoms in the cavity. Oscillations of the Rydberg positroniums are also considered. To perform a numerical estimates in a realistic case we wrote computer code, which can be adopted in any experimental setup. Its work is illustrated with an example of a planned positronium experiment within the AEgIS project. *